The present invention is directed to a chair having a seating platform, having a seat carrier that carries the seating platform and is connected to a central chair column or a plurality of chair legs, and having a rest carrier that proceeds toward the back under the seating platform and upward behind the seating platform and carries a backrest, whereby the seating panel, close to its front edge, is hinged to the seat carrier pivotable around a transversely proceeding, first swivelling axis and, offset therefrom toward the back, is hinged to the rest carrier pivotable around a parallel, second swivelling axis, whereby the rest carrier is hinged to the seat carrier pivotable around a third swivelling axis that proceeds between the first and second swivelling axis and parallel thereto, and whereby a compression spring arrangement that exerts a pre-stress force acting upwardly on the seating platform and toward the front on the back rest is provided under the seating platform and is supported thereat.
DE 43 13 301 C2 discloses a chair of the type just described. It is thereby specifically provided that supports that are downwardly directed in pairs are rigidly secured to the underside of the seating platform in the front and back region thereof, whereby the lower ends of the front supports are pivotably connected to downwardly directed guide members pivotably secured to the seat carrier, and the lower ends of the rear supports are pivotably connected to the rest carrier, and that the compression spring-arrangement is arranged between the seating platform and the seat carrier. What is referred to as a synchronous mechanism is achieved with this design of the chair, whereby, when the back part of the seating platform is loaded, the platform is lowered toward the back and the backrest is simultaneously pivoted toward the back, whereby the swivel angle of the backrest is usually greater than the swivel angle of the seating platform. The relationship of the swivel angle to one another is defined by the interacting lever lengths.
What is considered disadvantageous about this known chair is that the pre-stressing force of the back rest is dependent only on the strength of the compression spring arrangement and the lever effect determined in the design of the chair, so that an adaptation of the pre-stressing force of the backrest to different body weights of different users is not possible at all. Although an influencing of the pre-stressing force of the backrest would be possible by employing an adjustable or biasable compression spring arrangement, the user of the chair must manually implement the adjustment for this purpose, which represents an undesirably high outlay, particularly when a chair is used by different users that differ in weight. Moreover, it is not assured that the user will find the suitable setting, as a result whereof settings of the pre-stressing force of the backrest can derive that are incorrect and that may even be harmful to health under certain circumstances.
An object of the present invention is therefore to create a chair of said species that avoids the disadvantages that have been presented and whereby, in particular, an automatic adaptation of the pre-stressing force of the backrest to users differing in weight is achieved.
The features of the chair that are present in a preferred embodiment of the invention are that the seating platform is moved down given use by a heavy user, this necessarily leading to a tensing of the compression spring arrangement. Since the compression spring arrangement is supported on the extension of the rest carrier, the compression spring arrangement exerts a lever moment on the rest carrier that leads to an increase in the pre-stressing force of the backrest. A chair user having a high body weight thus experiences an increased support of his or her back by the backrest, as is desired and ergonomically meaningful. When a lighter weight user sits on the chair, the seating platform assumes a position that lies further up and wherein the compression spring arrangement is tensed less; correspondingly, a slighter pre-stressing force of the backrest necessarily follows, so that a lighter weight user also experiences an appropriately lesser supporting force of the backrest against his or her back in conformity with the lower body weight. At the same time, however, the synchronous adjustment of seating platform and backrest is preserved to its full extent, so that the seating platform and the backrest are also swivelled in a predetermined relationship relative to one another given changes in the sitting position. Despite the synchronous mechanism and the automatic adaptation of the pre-stressing force of the backrest to different user body weights, the chair has a surprisingly simple design, so that the manufacture of the chair is relatively simple and cost-beneficial.
In order to achieve a compact structure that occupies little space, it is preferably provided that the second swivelling axis proceeds under the seating platform close to the longitudinal center thereof. The mechanism required for the chair movements can thus be concentrated under the front half of the seating platform, which simplifies the manufacture of the chair and which yield an attractive appearance of the chair and, in particular, of its motion mechanism arranged under the seating platform.
It is also provided that the underside of the seating platform comprises at least one respective front and back bearing support through which the first, front swivelling axis and the second, back swivelling axis proceeds. As a result of these bearing supports, the first and the second swivelling axes are lent a desired spacing from the seating platform. Moreover, different seating platforms can be connected to the bearing supports in the simplest way, so that different embodiments and designs of the chair with a different seating platform are possible with little outlay.
A technically simple and, at the same time, functionally dependable solution for achieving the aforementioned vertical motional latitude of the seating platform relative to the seat carrier and/or the rest carrier is comprised therein that the bearing supports each comprise an oblong hole through which a first, front and second, back bearing pin rigidly connected to the seat carrier respectively proceeds, whereby the oblong holes proceed on a radius around the respectively non-appertaining, other bearing pin. As a result of said course of the oblong holes, a swivelling of the seating platform both around the front, first swivelling axis as well as around the back, second swivelling axis is possible without seizing, so that the seating platform can effortlessly adapt to different sitting postures of the chair user.
It is further proposed that, for forming a motion detent of the rest carrier, the second, back bearing pin also proceeds through an essentially vertically directed oblong hole in the rest carrier. Separate means for limiting the movement of the rest carrier are eliminated in this way, this being a further contribution to the simplification of the mechanical design of the chair. At the same time, said oblong hole, in interaction with the second, back bearing pin, serves for coupling the seating platform and rest swivel within the synchronous mechanism.
One embodiment of the chair, which can be preferably employed as an office swivel chair, provides that the seat carrier, proceeding in longitudinal direction of the seating platform, is arranged thereunder in the transverse center thereof, and has its back end connected to the chair column; that a respective rest carrier having a respective, appertaining compression spring arrangement is provided to the left and right of the seat carrier and symmetrically relative thereto; that two respective, front and back bearing supports are present; and that a respective, through, front and back bearing pin is attached to the seat carrier.
An alternative embodiment of the chair, which is essentially suitable as a consultation or conference chair, is characterized in that the seat carrier is implemented bipartite and is connected to a respective chair leg arranged proceeding in longitudinal direction of the seating platform laterally to the left and right thereof and thereunder as well as at its front and back ends; that a respective rest carrier with a respective, appertaining compression spring arrangement is provided at the left and right inside of and parallel to the two seat carrier parts; that respectively two front and back bearing supports are present; and that a respective, through, front and back bearing pin is attached to the two seat carrier parts.
Said compression spring arrangement is advantageously a coil spring arrangement because coil springs require little installation space and because they are a standard component part that can be accordingly easily acquired in the greatest variety of embodiments.
Alternatively, for example, the compression spring arrangement can also be a gas compression spring arrangement or an elastomer spring arrangement instead of a coil spring arrangement.
In a further alternative, the compression spring arrangement is formed by a torsion spring arrangement.
It is provided in a further development of the aforementioned embodiment of the chair that the/each torsion spring forming the torsion spring arrangement comprises a spring member that comprises one or more turns surrounding the third swivelling axis as well as two spring legs extending tangentially outward therefrom, whereby a first spring leg is supported close to its free end at the underside of the seating platform and a second spring leg is supported at the rest carrier, and whereby the spring legs are biased such that they exert an upwardly directed force onto the seating platform and exert a force on the rest carrier that pre-stresses the backrest toward the front. What this chair advantageously achieves is that the structural height of the spring arrangement is determined only by the outside diameter of the spring member since the torsion spring has a spring member whose longitudinal axis proceeds in horizontal direction transversely under the seating platform. At the same time, the spring member embraces the third swivelling axis, so that the torsion spring is adequately reliably held under the seating platform without additional structural measures. Further, it is unproblematically possible to set the spring characteristic of the torsion spring within broad ranges as desired, whereby changes in the spring characteristic are possible by modifications of the spring strength and/or the number of turns and/or the turn diameter as well as the length of the spring legs. One advantage, finally, is also comprised therein that torsion springs are simple and commercially available spring elements that are cost-beneficial and keep the overall manufacturing costs of the chair low.
It is provided in a preferred development, that both spring legs proceed toward the front away from the spring member approximately parallel to one another, whereby the second spring leg is supported at the upper side of the extension of the rest carrier and exerts a downwardly directed force onto the extension. This alignment of the spring legs yields an especially space-saving arrangement, so that the spring arrangement requires only a slight structural height under the seating platform. This is especially advantageous for the visual appearance of the chair in its side view.
In order to keep wear phenomena and noises in the use of the chair as low as possible or even avoid them to the farthest-reaching extent, it is also proposed that at least the first spring leg lies in a glide or roll guidance connected to the seating platform.
In order to distribute the forces acting on the parts of the chair in conjunction with the spring-bearing and thereby limit them in terms of their size, it is also proposed that two torsion springs are provided symmetrically relative to the longitudinal center axis of the chair, these being preferably formed of one piece with one another on the basis of a single, correspondingly doubly coiled and bent spring steel wire or rod. Due to the one-piece implementation of the two torsion springs, moreover, a further contribution can be made to a simple mechanical design and cost-beneficial manufacture.
In another alternative, the compression spring arrangement in the chair is formed by a torsion bar spring.
It is provided in a further development of the aforementioned embodiment of the chair that the/each torsion bar spring forming the torsion bar spring arrangement is formed with at least one spring section that is loaded for torsion and proceeds in the transverse chair direction and is formed with at least two spring levers proceeding in longitudinal chair direction, whereby a first spring lever is supported close to its free end at the underside of the seating platform and a second spring lever is supported at the rest carrier, and whereby the spring levers are biased such that they exert an upwardly directed force on the seating platform and exert a force on the rest carrier that pre-stresses the backrest toward the front.
The particular advantage of this chair is comprised therein that the compression spring arrangement requires only an extremely slight installation height, as a result whereof the component parts of the chair arranged under the seating platform, including the compression spring arrangement, can be implemented especially flat. As a result thereof, the side view of the chair is lent an especially elegant and light appearance without the stability and the functionality of the chair being deteriorated.
A further simplification of the design of the chair, as preferably provided, is achieved in that the spring section loaded for torsion simultaneously forms the first swivelling axis. A separate bearing pin for forming the swivelling axis is thereby eliminated, which advantageously reduces the number of discrete parts required.
It is also proposed that the spring levers of the spring sectionxe2x80x94as seen in a bottom view of the chairxe2x80x94proceed approximately parallel to one another andxe2x80x94as seen in a side view of the chairxe2x80x94proceed toward the back upon inclusion of an acute angle, whereby the second spring lever is supported at the upper side of the extension of the rest carrier and exerts a downwardly directed force on the extension. Given the fashioning and arrangement of the torsion bar spring described here, this also requires relatively little installation space in horizontal direction of the chair in the longitudinal direction thereof, so that a contribution to a compact structure is also made in this respect.
The torsion bar spring is preferably formed of one piece on the basis of a spring steel bar bent U-shaped. Such a torsion bar spring can be manufactured in an especially simple and cost-beneficial way and requires only slight material outlay, this contributing to a desired, low, overall weight of the chair.
In order to also achieve a distribution of the forces of the compression spring arrangement occurring upon use given this chair, it is also proposed that two torsion bar springs are provided symmetrically relative to the longitudinal center axis of the chair, these being preferably formed of one piece with one another on the basis as a single spring steel bar that is bent cam shaft-like.
The front and the back swivelling axis serve for connecting the seating platform to the seat carrier, to which end the seating platform usually comprises bearing supports at its underside. For all chairs implemented with bearing supports, the invention proposes that respectively two left and two right bearing supports are present, these being respectively implemented combined and of one piece to form a left and a right support component part or even to form a single support component part. This measure simplifies the manufacture of the chair and enhances the stability of the bearing of the seating platform at the seat carrier and at the rest carrier.
The invention also provides that the seat carrier and at least that part of the rest carrier proceeding under the seating platform as well as, potentially, the bearing supports are punched and pressed parts of sheet steel. Punched and pressed parts of sheet steel can be especially cost-beneficially fabricated in large unit numbers as mass-produced parts, whereby they exhibit high stability and durability at the same time. A high and also durable quality of the chair is thus assured given low manufacturing costs and given low wear.
As explained above, the chair preferably has a combination of synchronous mechanism and weight-dependent pre-stressing of the rest. For users who do not wish the synchronous mechanism, the chair can also be alternatively implemented such that the articulation of the seating platform to the rest carrier is omitted, as a result whereof the seating platform and the rest carrier can be swivelled unsynchronized, i.e., independently of one another. The technical modifications required for this purpose are advantageously limited to the omission of individual parts.